1. Field of the Invention
The present invention relates to an electron emission device, and more particularly, to an electron emission device and an electron emission display having a beam-focusing structure using an insulating layer.
2. Discussion of Related Art
Generally, an electron emission device can be classified into a hot cathode-type and a cold cathode-type. The hot cathode-type and the cold cathode-type employ a hot cathode and a cold cathode as an electron emission portion, respectively.
Also, a cold cathode-type electron emission device can have a structure such as a field emitter array (FEA), a surface conduction emitter (SCE), a metal insulator metal (MIM), a metal insulator semiconductor (MIS), a ballistic electron surface emitting (BSE), etc.
The electron emission device having the FEA structure is based on a principle that when a material having a low work function and/or a high beta(β)-function is used as an electron emission portion in a vacuum, electrons are easily emitted from the material due to an electric field difference. Such electron emission device having the FEA structure employs a tip structure mainly containing molybdenum (Mo), silicon (Si), a carbon material (e.g., graphite, diamond-like carbon (DLC), etc.), and/or a nano material (e.g., a nanotube, a nanowire, etc.) as the electron emission portion.
The electron emission device having the SCE structure is provided with an electron emission part in which a first electrode and a second electrode opposing each other are formed on a first plate, and a conductive layer is formed between the first electrode and the second electrode. The conductive layer is formed with a minute crack or gap, thereby forming the electron emission part. Such electron emission device is based on a principle that the electron emission part formed by the minute crack or gap emits electrons when electric current flows through a surface of the conductive layer by applying voltage to the first and second electrodes.
The electron emission device having the MIM or MIS structure includes an electron emission portion having a metal-insulator-metal structure or a metal-insulator-semiconductor structure, and is based on a principle that electrons are emitted from the metal or the semiconductor of high-electric potential to the metal of low-electric potential when a voltage is applied between the metal and the metal or between the metal and the semiconductor.
The electron emission device having the BSE structure is based on a principle that electrons travel without sputtering when the size of a semiconductor is smaller than a mean free path of the electrons contained in the semiconductor. Such electron emission device includes an electron supplying layer made of a metal or a semiconductor and formed on an ohmic electrode, an insulator formed on the electron supplying layer, and a thin metal layer formed on the insulator, so that the electrons are emitted when a voltage is applied between the ohmic electrode and the thin metal layer.
The foregoing electron emission devices are employed in electron emission displays, backlights, lithography electron beams, etc.
In the aforementioned electron emission devices, the electron beam emitted from the electron emission portion spreads in a voltage-applied direction. Therefore, there is a need for a focusing electrode to focus the electron beam. An example of an electron emission device with the focusing electrode is disclosed in Korean Patent Publication No. 2002-32208. Hereinafter, the conventional electron emission device with the focusing electrode will be described with reference to FIGS. 1 and 2.
FIG. 1 is a schematic plan view of a conventional electron emission device with a horizontal focusing electrode.
As shown therein, the conventional electron emission device includes a plurality of micro-tips 1 respectively formed inside a plurality of gate holes 2, a gate electrode 3 formed above the micro-tips 1 and determining an emitting direction of electrons emitted from each micro-tip 1, and a focusing electrode 4 to focus the electrons emitted from the micro-tips 1.
In the conventional electron emission device, to enhance a focusing effect, a distance between at least one of the micro-tips 1 used as an emitter and the gate electrode 3 should be short, and, at the same time, a distance between the gate electrode 3 and the focusing electrode 4 should also be short. Because of this, the fabricating process for the conventional electron emission device is difficult. Also, when the focusing electrode 4 is horizontally arranged, the number of emitters per unit surface area is limited.
FIG. 2 is a sectional view of a conventional electron emission device with a vertical focusing electrode.
As shown in FIG. 2, the conventional electron emission device includes a plate 202, a first insulator 203, a gate electrode 204, an emitter 205, a cold cathode 206, a second insulator 207, a focusing electrode 208 and a metal mesh 210. In this electron emission device, in order to focus an electron beam from the emitter 205, a voltage of −40V is applied to the focusing electrode 208 and a voltage of 80V is applied to the gate electrode 204. Here, the voltage applied to the gate electrode 204 serves to control the amount of beam current.
Such conventional electron emission device with the vertical focusing electrode is excellent in focusing the electron beam, but has a complicated fabricating process because the insulator formed on the gate electrode should be thick with a thickness of a few μm to a few hundreds μm, thereby lowering a yield thereof.